The invention relates to a process for the continuous heat setting of yarn laid down in loops, which yarn is fed along a transporting section with a predetermined transport speed through a heat setting chamber of predetermined length and operating with superheated steam, in which a chamber temperature prevails which is constant along a part of the transport length and which is set above the required heat setting temperature.
A process of this kind is disclosed in the U.S. Pat. No. 4,513,514. This patent describes an installation for yarn conditioning of the type GVA 2500, which is sold by the firm Maschinenfabrik Michael Horauf, D-73072 Donzdorf, Federal Republic of Germany, assignee of the present application.
This known process, which is preferably applied for the heat setting of carpet yarns, works in a so-called open system with superheated steam and atmospheric pressure. The temperature in the heat setting chamber lies significantly over that required for heat setting and serves first and foremost the purpose of heating the yarn to be heat set quicker to the heat setting temperature. Due to the yarn being laid down on the transport belts, not all parts of the yarn reach the heat setting temperature simultaneously; some parts of the yarn can thus exceed the heat setting temperature and in certain circumstances be damaged as a result. If, in attempting to exclude the possibility of any damage, the dwell time of the yarn in the heat setting chamber is shortened, it can happen that some parts of the yarn will not reach the required heat setting temperature. In the known process therefore, the individual parameters, namely yarn density, chamber temperature, transport speed, steam content and steam flow rate, must all be exactly observed.
An object of the invention, in the case of a process of the above mentioned type, is a flawless handling of the yarn and thus an avoidance of yarn damage.
This object is achieved in that the chamber temperature is set at a level just above the heat setting temperature,and the transport speed and chamber length are so adjusted that the yarn, having reached the heat setting treatment, essentially retains that temperature for a part of the transport length.
As the chamber temperature lies only minimally over the treatment temperature of the yarn, for example the heat setting temperatures, damage resulting from overheating, which leads to oxidization on the yarn or on the softener, is certainly avoided. The chamber temperature is kept so low that the heat setting temperature, as soon as the yarn has reached it, remains constant for the rest of the dwell time. The chamber extends to a length which guarantees that even yarn parts which do not lie advantageously reach the heat setting temperature. No damage is done when those yarn parts which reach the heat setting temperature earlier remain at this temperature for a while longer, as a harmful excess in temperature is practically impossible.
The process according to the invention has the further advantage that it is not dependent on so many adjusting parameters. Furthermore, energy consumption is reduced because of the lower chamber temperature.
According to the invention, the part of the transport length with a constant chamber temperature is equal to three quarters of the chamber length. As is known, the constancy of the chamber temperature is affected by the entry and exit openings for the transport device, which is led through the heat setting chamber. As a somewhat longer dwell time is now not harmful, the heat setting chamber can be designed to be longer than it has been up to now. This results in a better use of the area with constant temperature, as the part of the chamber length where the chamber temperature sinks due to the entry and exit openings is shorter, in relation to the entire chamber length. For example, if the chamber length is doubled, the length where a constant temperature prevails is trebled. An extended chamber can also be used advantageously in that the transfer density of the loops of the yarns can be reduced, which in turn leads to the critical yarn parts reaching the heat setting temperature quicker.
The chamber temperature is advantageously set at a level which lies at most 10.degree. Celsius above the heat setting temperature. It would be ideal if the heat setting temperature was also the chamber temperature, but this however cannot be attained in practical cases. An effort is made however to keep the chamber temperature as low as possible, so that the yarn just about reaches its heat setting temperature. In this case, it is irrelevant if the dwell time is exceeded by a certain amount; damage to the yarn is practically impossible.
In the case of a heat setting chamber for carrying out the process, which chamber comprises entry and exit openings for the transport belts transporting yarn, a feeding pipe for supplying steam, a heating system for superheating the steam as well as a plurality of fans, arranged beside each other in transport direction, for generating a circulating current of steam and set transversely to the transport direction, more than four fans are provided, of which the two fans arranged nearest the entry and exit openings have a rotational direction which is set against the allocated entry and exit openings. The parts in the heat setting chamber in which the chamber temperature sinks due to the entry and exit openings are kept smaller, thus using the chamber length more advantageously for the heat setting of the yarns.
In a preferred development of the invention the heat setting chamber comprises two single chambers, which are connected to each other by a heat intermediate zone. This leads to a series of advantages. Firstly a standard chamber can be used, which can itself, or in combination with another single chamber, be connected to an extended heat setting chamber. Secondly, the heat setting conditions are easier to control in a reduced single chamber. In addition, when required a process can be executed whereby different temperatures prevail in the two single chambers.
The single chambers have for this purpose the same form and are symmetrically arranged in relation to the intermediate area.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.